Aviation spark plug



S'pt 26, 1944- J. DEVINE AVIATION SPARK PLUG' (RADIO SHIELDD) Filed Oct. 5, 1942 ....nln ...5.1.

INVENTOR ATTORN EY PatentedSepL26,l944

UNITED STATES PATENT ol=l=lcE :,asaau svm'rron seam; PLUG (aspro smELnEn) .ruim Devine, New York, N. Y. applicaties october s, 1942, serai No. 460,76:

1o claims (ci. 12a-169) My invention relates to spark-plugs, and more particular to spark plugs of the shielded type,

which are used in aviation motors.

The principal objects of my invention are to produce a gas-light seal between the central electrode and the ceramic core-memhe to relieve longitudinal wall of the shank of said electrode I is slightly tapered. so that the inner end-part l of said longitudinal wall is of greater transverse diameter than the outer end-part l of said longitudinalwall.

, A c0llper`rod 2 is electrically bonded to the wall of the recess of said electrode I, in order to conduct theheattotheilring head 3,so asto keep the plug at proper and normal operating temperature. The outer longitudinal end of the shankotsaidelectrodehasathread l.

The ilring-head I is enlarged relative to the shank of said electrode I, thus providing a shoulder, on which a mica washer I is located. Rearwardly of said mica washer 1, said shank of the electrode I is provided with helically wound mica insulation I, the inner end o! which abuts washer 1.

An outer mica washer Il abuts the outer end of insulation l. Said outer mica washer Ill abuts the inner end-wall ot the ceramic core-member 0. Acontact terminal cap II' is screwed upon thread l. Saidterminalcap II maintains the assembly between core-member l, electrode I, washers 'I and Il and insulation l. The inner hollow end-portion ot the shank of electrode I is peened overthe inner end-wall of terminal can Il, so that slid. tisht assembly is reliably maintained.

Ineiiect, the mici. washers 'I and Il," are extensions of the mica insulation I. The insulating members can be made wholly or partially of ilexibleinmlatingmaterialotherthanmica. such as a solid alkyd resin.

A gas-tight seal is thus produced by tlm insulation, between the electrode I and the ceramic core-member I. The bore of said core-member iistaperedtocorrespondtothetaperofthe outer longtiudinal wall of the shank of the electrode I, and the insulation 8 is also correspondingly tapered.

'Ihe device ot Fig. 3 is substantially the same in principle, as the device ot Fig. 1. In Fig. 3. the outer longitudinal wall of the shank of the electrode I, is tapered so that the transverse diameter of the'inne'r end-portion I2, is less than the transverse diameter of the outer end-portion I3. Y

In Fig. 3, the mica insulation Il, which corresponds to the mica insulation I, terminates about one inch from the outer end of the,shank of the electrode I. Outwardly of the insulation Il, there is a sleeve of moisture-absorbing cement I5, whose outer end abuts the outer mica washer IB 1 rig. 1 shows a uns mem sneu n, preferably made of copper, which has an inner frusto-con ical end-portion, which abuts the corresponding part of the outer wall of the ceramic core-member 9.

In Fig. 3, additional ilexible mica insulation i1 is located in abutting relation between the metal shell It and the core-member l.

The outer end-portion of said metallic shell I6 is crimped over a metal gasket 2l, which is located on shoulder l! oi' the core-member I.

A metal ring 2l abuts the crimped end-portion of shell Il.

As shown in Fig. 2, a metal shielding sleeve 22 has a. threaded portion 23 which is screwed into the threadl of the bore o! metal shell 24. The inner end-wall of metal sleeve 2 2, abuts a metal washer 2l, which abuts the metal ring 2l. The

40 ring 2| is forced tightly into position. A hard ceramic sleeve 25 is located in metal sleeve 22.

Said sleeves 25 and 22 are separated by a iiexible insulator 26, which is preferably made of mica, so that it can be helically wound. The inner end of insulation 26 abuts the metal washer 21.

Said insulator 28 minimizes or prevents the cracking of the hard inner ceramic sleeve 25 and it produces a tight seal between sleev 2i and 2f. Said ilexible insulator 2l also relieves vibration.

Themetal sleeve 22isashield,lnordertopre vent the transmission or electrical disturbances from the spark.plug, to an adjacent radio receiving set.

The combination of flexible mica insulation and of hard ceramic insulation. is of great value.

The fuels which are now used in internal combustion engines ot the high-compression type, act

injuriously upon mica. However, mica does not crack under heat, while ceramic insulationdoes crack. The ceramic insulation protects the mica insulation, andthe mica insulation minimizes the cracking o! the ceramic insulation. Even if the ceramic insulation does crack, the mica insulation will keep the plug functioning for a substantial period.

The thin metal housing i 6, which is preferably made of copper is'connected to theceramic core il. so as to produce a gas-tight Joint.l This thin metal housing compensates for irregularities in the ceramic core-member 9, thus producing a gas-tight Joint with the metal shell 26.

Fig. 2 shows the gas chamber 29, the grounded electrode 3d, and the firing-gap t i The additional ilexible mica insulation i7, protects the core-member Strom stresses which are produced when the metal ring 2i is forced into position. However, the use of such additional insulation il is optional.

The mica insulation used herein, is of the type known. as cigarette mica. This is flexible and compressible.

As shown 'in Figs. l and 3, I provide a subassembly of the electrode and core-member by means of nut ii, which compresses the tapered mica insulation between the correspondingly tapered proximate longitudinal walls of the electrode and the core-member. The crimped part of housing it, with or without the insulation il,

ascaoi to said core-member, said nut having an endwall which is `proximate to the respective endwall of said core-member, compressible insulating means located between and abutting the aforesaid proximate walls. said nut maintaining said insulating' means under compression to provide a gas-tight seal between each said pair of proximate walls.

3.-For use in a spark-Plug. the sub-combination oi a hollow and rigid core-member made of insulating material, an electrode located in said core-member,7 at least one end or said electrode projecting from said core-member, said electrode being spaced wholLv from said core-member, compressible spacing means made of insulating material and spacing said electrode from said coremember, assembly means connected to one of the elements of said sub-combination and holding saidspacing means under pressure and holding said core-member and electrode in ixed relation.

4.. In a spark plug comprising a shell a centrai electrode, a mica insulator encircling said electrode, a secondary insulator comprising ci' ceramic having an outer shoulder encircling said mica insulator, a copper housing having an annular bore encircling said ceramic insulator and crimped over the outer shoulder of the said ceramic insulator, a copper conductor through the Iii provides a gas-tight it between said crimped part and the respective shoulder of the core-member.

I vhave shown perferred embodiments of my inven-tion, but it is clear that numerous changes and omissions and additions can be made without departing from its scope.

' I claim: l. For use in a spark-plug, the sub-combina` tion of a rigid core-member made of ceramic insulating material, said core-member'being hol= low, an velectrode located in said core-member, said electrode having a ring end which projects outwardly of said core-member, the proximate longitudinal walls of said electrode and of corecenter of said central electrode to conduct excemive heat from the firing electrode head to the cooler part of the plug and to conduct excessive heat from the gas chamber by the use of the copper housing encircling the ceramic insulator.

5. In a spark plug having a cylindrical nut engaging a shell, and tapered central electrode extending therewith, a mica sleeve, having an outer taper encircling said tapered electrode, a

` ceramic member having a shoulder on the outer surface encircling said insulator sleeve, copper housing having an inner annular surface encircling the said mica sleeve, the said copper A housing having an annular outer surface to regmember being correspondingly taperedcompres sible insulation means located wholly between and wholly abutting said proximate Walls, assembly means holding said electrode and core-member in xed relation and maintaining said insulation means under pressure and in contact with said proximate walls to produce a gas-tight seal bei tween said proximate walls; said assembly means ;v

being xed to one of said elements of said sub :f

combination, said proximate Walls extending substantially to said ring-end.

2. For use in a spark-plug, the sub-combina-l tion of a rigid core-member which is made of in sulating material, said core-member having a longitudinal through-and-through bore, an electrode located in said bore and extending longitudinally outwardly beyond each end of said bore,

one end of said electrode having an enlarged head which is external to said core-member, said head having an end-wall which is proximate to and which is spaced from the respective end-wall of y said core-member, said electrode and said bore having proximate walls which are correspondingly tapered, the end-portion of said electrode which is opposed to said enlarged head having a thread which is external to said core-member, a nut seated on said thread, said nut being external ister'with an annular seat in the shell to act as shock absorber to the ceramic and to relieve the mechanical stress on the ceramic when thev latter is pressed in against the annular seat in the shell by the action of the threaded cylindrical nut.

6. Ina spark plug comprising a mica insulator sleeve tapered inwardly to engage a tapered electrode, a ceramic member having an inner taper to engage the said mica sleeve outwardly and an outer taper having a shoulder at its upper end to engage a copper housing member, the largest part o f said housing member is crimped over the shoulder of said ceramic to eiect a' gas-tight seal between the shoulder of said ceramic member and said crimped part of the copper housing.

` 7. In a spark plug an -annular ceramic insu= lator having an electrode ltherein an annular copper housing member having an'annular bore to register with said annular ceramic memberl and interposing means preferably mica between the.inner surface of the said annular copper housing member and the outer surface of said annular ceramic member and so arranged as to have the upper part of said copper housing member crimped over a shoulder of the ceramic member to eectfa gas-tight seal on top of the said ceramic shoulder.

8. In a spark plug comprising a tapered mica insulator inwardly tapered to engage a tapered electrode, a ceramic member having an inner taper to engage the said mica insulator, said ceramic member having an outer shoulder to engage a copper housing extending above the ceramic shoulder and crimped over said ceramic shoulder of said ceramic member to effect a gas tight seal between the copper housing and said ceramic member over said ceramic shoulder.

9. In combination with a spark plug a tubular metallic shield threaded at its lower end to screw into an opening of a hollow metallic shell, a ceramic core member seated within said metallic shell, and a tubular ceramic member seated Within said metallic shield, compressible insulation means within said ceramic core member, together with compressible insulation means sleeved longitudinally about said tubular ceramic member and being in intimate contact therewith and which means together serve to support and protect said ceramic members from cracking under intense heat and sudden atmospheric change.

l0. In combination with a spark plug, a tubular metallic shield threaded at its lower end to screw into an opening of a hollow metallic shell, a ceramic core member seated within said metallic shell and a tubular ceramic member within said metallic shield, compressible insulation means secured longitudinally within said ceramic core member and compressible insulation means secured about said tubular ceramic insulator outwardly to support, seal, and protect the said ceramic members from metallic stress, intense heat, and atmospheric change.

JULIUS DEVIN'E. 

